1. Field of the Invention
The present invention relates to a plasma display panel (PDP) device, and more particularly to a plasma display device for preventing from generating unevenness of luminance due to voltage drop in discharge electrodes or a driver circuit caused by a discharge current during a sustain discharge period.
2. Description of the Related Art
A PDP device has been expected as a display device having a panel, of which luminance is higher than that of a liquid crystal panel, having a wide angled field of view. In particular, an AC-type surface discharge PDP device having three electrode structures for full color display has been actively developed.
In a driving method of the PDP device, discharges is generated between address electrodes and X or Y electrodes provided faced to the address electrodes in an address period, depending on display data, so that wall charges are formed on cells. In a sustain discharge period, surface discharges are then repeated for the cell where the wall charges are accumulated by applying an AC voltage between the X and Y electrodes in the sustain discharge period. A gray scale can be displayed on each cell by controlling a number of the surface discharges according to its gradation.
It is called a sustain discharge to repeat generating the surface discharges by applying the AC voltage between the above described X and Y electrodes. The sustain discharge voltage is set so as that the sum of the voltage generated by the wall charges accumulated in the address period and the sustain discharge voltage would be a sufficient value enough to generate a new discharge and to keep the wall discharges.
A discharge scale becomes different according to the voltages applied between the X and Y electrodes on the cells in the sustain discharge period. As the applied voltage is higher, the charge scale becomes larger, and luminance for light-emission becomes larger. However, since the discharge currents flows between X and Y electrodes in the sustain discharge period, the total value of the discharge currents becomes different according to a number of the cells where the discharge occurs on the same X and Y electrodes. As the number of the discharged cells becomes larger, therefore, the discharge current becomes larger, thus increasing voltage drops on the X, Y electrodes and driver circuits. As a result, even if the same sustain discharge voltage is applied between the X and Y electrodes, the applied voltages in the cells become different and the generated luminance becomes different case by case. This results in displaying the luminance differed from a prescribed luminance, and causes unevenness of the luminance. It is not preferable to use as a display device.
In the conventional device, it has been proposed to control the number of the sustain discharges by detecting the number of the discharged cells to prevent the unevenness of luminance. For example, a circuit for controlling the number of the sustain discharges has been proposed in the Japanese Unexamined Patent Publication No. 9-68945. However, the proposed circuit is complex, and therefore, there is a demand to further improve the circuit.
Additionally, it has been proposed in the Japanese Patent Application No. 9-185343, for example, that similar voltage drop occurs in the X electrode driving circuit for commonly applying the voltages to the X electrodes in the sustain discharge period, it is prevented from generating the unevenness of luminance in each sub-field thereby. The PDP device according to the invention is also employed to count the number of the discharged cells in each sub-field and correct the sustain discharge periods according to the number of the discharged cells. However, the PDP device according to the later case can cope with the unevenness of luminance between sub-fields, but it can not solve the problem of the unevenness of luminance within a display panel at the same sub-field.
As are described above, the circuitry structures in the conventional methods have complex structures, and therefore, the unevenness of luminance on each cell can not be prevented.
Accordingly, it is an object of the present invention to provide a PDP device, by which unevenness of luminance can be prevented on each cell, with a simple circuitry structure.
It is another object of the present invention to provide a PDP device for preventing from generating unevenness of luminance in each cell or each display line, according to a number of the sustain discharged cells, i.e., a display load rate at a sustain discharge period.
It is another object of the present invention to provide a PDP device, by which required luminance can be automatically compensated according to insufficiency of luminance.
To achieve the above-described objects, the plasma display device according to the present invention employs a phenomenon where voltage drops applied to cells become larger according to a display load rate at a sustain discharge period, the luminance becomes lower and wall charges accumulated on the cells after the sustain discharge becomes lower as well. In other words, the present invention is characterized in that a prescribed erase pulse and sustain discharge pulse are applied to X and Y electrodes in the sustain discharge period. When the display load rate is lower, a scale of the sustain discharge at each cell is larger and the amount of wall charges at each cell is not lower. Therefore, the plasma display device according to the present invention selectively erases, by applying the prescribed erase pulse, only the cells where a scale of the sustain discharge is large enough to generate sufficient luminance, and compensates the luminance, by generating the sustain discharge due to the sustain discharge pulse thereafter, for the cells where a scale of the sustain discharge is small not enough to generate the sufficient luminance.
The above-described objects can be achieved by a plasma display device having a display panel including plural cells being selectively discharged according to display data and a driver circuit for driving the display panel, wherein the driver circuit causes an address discharge at a cell according to the display data, causes a sustain discharge at the cell where the address discharge is generated by applying sustain discharge pulses alternatively between X and Y electrodes provided along display lines, and further causes a luminance compensation discharge at, at least, a part of the cells by applying an erase pulse and an additional sustain discharge pulse following to the erase pulse between the X and Y electrodes.